This invention related to a method for preparing improved foamed phenol-aldehyde condensates. More particularly, this invention relates to a method for preparing phenol-aldehyde condensate foams which are substantially free of splits, voids or blow holes and which have an increased uniform cell structure.
Phenol-aldehyde condensate foams, commonly called phenolic foams, generally are produced from resole resins rather than novalac resins. Resole resins, also known as Stage A resins or One-Step resins, are produced by the condensation reaction of approximately equal parts of phenol and an aldehyde in the presence of a basic catalyst. This reaction produces a complex mixture of condensate of phenol and the aldehyde which are soluble in alkali, alcohols, ketones and water to a degree. The resoles can react further to form resitols, Stage B resins, and resites, Stage C resins which are insoluble and infusible. Novolac resins are acid catalyzed condensates with a phenol to aldehyde ratio greater than one. These resins have very little, if any, cross-linking and are permanently fusible and soluble resins. Novolac resins are sometimes used in combination with resole resins in the production of phenolic foams and novolac resins can react further with aldehydes under basic conditions to produce resite-like products, but they are not usually used by themselves to produce phenolic foams.
Phenolic foams are all mostly of the rigid type and they are usually considered as having from about 40 to 60 percent open cells. Phenolic foams have advantages over other foamed resins such as polyurethane resin foams, in cost, thermal stability, fire resistance, resistance to humidity, chemical resistance, dimensional stability, smoke generation, electrical properties, and adaptability to foaming in place. The distribution pattern between open and closed cells also gives phenolic foams a certain amount of sound-insulation value as well as good thermal insulation. The phenolic foams also have a good density good of from less than 1 pound per cubic foot to about 80 pounds per cubic foot.
The desirability of producing phenolic foams for various applications has been recognized. These phenolic foams would be useful in the insulation market and the adoption of foamed-in-place phenolic insulation would be advanced appreciably by the development of equipment for continuous formation of phenolic foam.
Despite the above advantages and generally favorable economics, phenolic foams have not penetrated the insulation market. This is the result of the problem with current-day phenolic foams in that they have ruptured cell walls and splits and/or voids in the center of the foamed mass and they are subject to cavitation caused by blow holes or channels.
The art has proposed several methods for overcoming the above enumerated disadvantages of phenolic foams. One method includes the addition of nitrogen compounds, such as heterocyclic nitrogen-containing compounds like 2,3-N-methylpyrrole, to the resole resin to be foamed. Also, another method involves the use of certain blowing agents like polyhalogenated fluorocarbons to overcome the above mentioned disadvantages.
In U.S. Pat. No. 3,704,269 (Freeman et al.) a process is disclosed for preparing an insoluble, infusible cellular foam by reacting one part by weight of an aldehyde condensation polymer with active alkylol groups with 0.05 to 2.0 parts by weight of a nitrogen compound to produce a liquid resin. The nitrogen-containing compound is selected from substituted primary aromatic amines, substituted bis(aminoaryl) compounds, aminonaphthalenes, heterocyclic nitrogen-containing compounds, selected from the group consisting of 2,3-; 2,4-; 1,6-; or 3,4-diaminopyridine, pyrrole; N-methylpyrrole; 2,4-dimethylpyrrole, or 4,6-diaminopyrimidines. Then an alkylene donor like an aldehyde and a foaming agent are added to the liquid resin, and the resin composition is expanded to produce a foam product.
In U.S. Pat. No. 3,389,094 (D'Alessandro), closed-cell phenolic foam structures of fine cell size are provided by foaming a phenol-formaldehyde resin containing less than 10% water with a polyhalogenated fluorocarbon foaming agent. The fluorocarbons display an unusual and unique solubility phenomenon in the resole resin. They are uniquely soluble during the initial stages of the condensation thereby providing for uniform distribution of the blowing agent resulting in a longer vaporization period which is the probable cause of the fine cell structure of the foams. This patent also teaches that upon addition of the fluorocarbons to the resin mix there is no dilution effect and there is often an appreciable increase in viscosity. Such an increase in viscosity appears to be a contradiction to the teaching that the fluorocarbons are uniquely soluble in the resin mix.
It is also well known in the art of plastic foams as disclosed in U.S. Pat. No. 3,210,300 (Leibu et al.) to prepare polyether and polyurethane foams that are open celled and resilient with the use of a cell regulator. The cell regulator is an alkylated amine, or a mixture of an amide and a low molecular weight aliphatic sulfoxide, or a mixture of an amide and a low molecular weight sulfone. The preferred amides are N-methylpyrrolidone; N,N-dimethylacetamide, and espcially N,N-dimethylformamide. These cell regulators are used in a one-shot foaming technique in either batch or continuous processes. Generally the cell regulator should not be mixed directly with the diisocyanate but it should be added simultaneously with other ingredients to the diisocyanate or it should be added to a mixture of ingredients which are then added to the diisocyanate. The greater the amount of cell regulator employed, the greater will be the permeability of the resulting foam. The increase in permeability with larger quantities of cell regulator appears to result from a more complete removal of the membrane-like films or windows between cells.
The invention described herein is an improvement over the prior art because the prior art fails to teach how to make a phenolic foam that does not have the majority of its cell walls ruptured and is substantially free of splits and voids in the center of the large mass of foam or on the surface of the foam.